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Both would be below .02% limit for drivers under legal drinking age of 21

Test checks only for alcohol; DUI law also prohibits impairment by controlled substances

Chief: Bieber said he drank, smoked pot, took prescription medication before driving Thursday

Two breath tests estimated pop star Justin Bieber's blood-alcohol content was below .08% after his arrest on suspicion of driving under the influence in Florida, a source close to the investigation said Friday.

The tests indicated contents of .011% and .014%, the source said. Both would be below the general .08% legal limit for drivers and Florida's .02% limit for drivers under the legal drinking age of 21. Bieber is 19.

It's not clear how soon after the arrest the tests were given. And an alcohol level by itself wouldn't necessarily clear a defendant of DUI, as Florida law also says people can be convicted if controlled substances -- not just alcohol -- impair the driver's "normal faculties."

Police said Bieber admitted to drinking, using marijuana and taking prescription pills before his arrest early Thursday in Miami Beach. He also failed a field sobriety test, Miami Beach police said.

Bieber was pulled over after a Miami Beach officer saw him driving a yellow Lamborghini in a race against a red Ferrari in a residential area of Miami Beach, city Police Chief Raymond Martinez said.